1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to encoding and decoding of audio, and more particularly, to an audio encoding method and apparatus, and an audio decoding method and apparatus, for processing a death sinusoid and a general continuation sinusoid in different ways.
2. Description of the Related Art
Parametric coding is a coding method of representing audio with specific parameters, and the parametric coding is used in the Moving Picture Experts Group 4 (MPEG-4) standard.
FIG. 1 is a block diagram for describing a parametric coding method according to the prior art. In the parametric coding method, an input signal is analyzed and parameterized. In detail, an input audio signal is filtered (audio reading and filtering). By analyzing the input audio signal using three analysis methods, such as transient analysis, sinusoid analysis, and noise analysis, parameters corresponding to audio components in respective areas are extracted. The transient analysis corresponds to a change of very dynamic audio. The sinusoidal analysis corresponds to a change of deterministic audio. The noise analysis corresponds to a change of stochastic or non-deterministic audio. Then, the extracted parameters are formatted into a bitstream.
A sinusoid extracted by the sinusoidal analysis is also called a partial.
After the sinusoidal analysis is performed, tracking of the sinusoid is performed in order to perform Adaptive Differential Pulse Code Modulation (ADPCM) or Differential Pulse Code Modulation (DPCM) on the sinusoid. The “tracking” means that sinusoids continuing between sinusoids included in previous and subsequent frames are found and a correlation between them is set.
A sinusoid of a current frame, which cannot be tracked from sinusoids of a previous frame, is called a birth sinusoid or a birth partial. The terminology “birth” means that a sinusoid is not continual from a sinusoid of a previous frame and is newly born, i.e. created, in a current frame. For a birth sinusoid, difference coding using a sinusoid of a previous frame cannot be performed, and thus, absolute coding must be performed. Thus, a number of bits are necessary for coding.
On the other hand, a sinusoidal component of a current frame, which can be tracked from sinusoids of a previous frame, is called a continuation sinusoid or a continuation partial. Since difference coding using a sinusoid of a previous frame can be performed for a continuation sinusoid, efficient coding can be performed.
A sinusoid, which is not continual with a sinusoid of a subsequent frame and disappears from among continuation sinusoids, is called a death sinusoid or a death partial.
FIG. 2 is a diagram for describing a death sinusoid.
Referring to FIG. 2, death sinusoids 3, 5, 7, 9, 11, 13, and 15 are illustrated.
For the death sinusoid 3, tracking starts from a birth sinusoid 1 that is connected to a continuation sinusoid 2, and the tracking ends at the death sinusoid 3.
In a conventional audio encoding method, such a death sinusoid is not particularly considered. Thus, the same encoding as that of a general continuation sinusoid is applied to such death sinusoids.
FIG. 3 is a flowchart illustrating an audio encoding method according to the prior art.
Referring to FIG. 3, a sinusoid is extracted by performing sinusoidal analysis, in operation S10, and by performing sinusoid tracking, in operation S20, to determine whether the extracted sinusoid is connected to a sinusoid of a previous frame. If it is determined, in operation S20, that the extracted sinusoid is not connected to the sinusoid of a previous frame, the extracted sinusoid is determined to be a birth sinusoid. However, if it is determined, in operation S20, that the extracted sinusoid is connected to the sinusoid of a previous frame, the extracted sinusoid is determined to be a continuation sinusoid. Then, additional consideration for a death sinusoid is not performed.
The extracted sinusoid is quantized, in operation S30, and it is determined in operation S40 whether the sinusoid to be encoded is a birth sinusoid. If it is determined, in operation S40, that the sinusoid to be encoded is a birth sinusoid, absolute coding is performed for an amplitude component, in operation S50. This absolute coding is called birth amplitude coding. If it is determined, in operation S40, that the sinusoid to be encoded is not a birth sinusoid, a difference between the amplitude component of the sinusoid and an amplitude component of a continued sinusoid of a previous frame is obtained and is coded, in operation S60. This difference coding is called continuation amplitude coding.
As described above, in the conventional audio encoding method, a death sinusoid is not particularly considered. However, since the death sinusoid has a unique characteristic, if the unique characteristic is used, a more efficient audio coding can be performed. Thus, the present invention will use the unique characteristic of a death sinusoid to perform a more efficient audio coding.